Transitioning from mimo to siso to save power

ABSTRACT

Various example embodiments are disclosed. According to an example embodiment, an apparatus may include at least one processor and at least one memory. The at least one memory may include computer-executable code that, when executed by the processor, is configured to cause the apparatus to send a message to a node in wireless communication with the apparatus, the message indicating a transition by the apparatus from multiple-input multiple-output (MIMO) to single-input single-output (SISO), and transition from wireless MIMO communication with the node to wireless SISO communication with the node after sending the message to the node.

PRIORITY CLAIM

This Application claims the benefit of priority based on U.S.Provisional Application No. 61/406,319, filed on Oct. 25, 2010,entitled, “Transitioning From MIMO To SISO To Save Power,” thedisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

This description relates to wireless communication devices.

BACKGROUND

Wireless communication devices may be disconnected from external powersources. As such, their available power, typically supplied by abattery, may be limited.

SUMMARY

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing two nodes in wireless communicationaccording to an example embodiment.

FIG. 2 is a vertical time sequence diagram showing communication betweenthe two nodes according to an example embodiment.

FIG. 3 is a diagram of a management frame according to an exampleembodiment.

FIG. 4 is a diagram of a data frame according to an example embodiment.

FIG. 5 is a block diagram of an apparatus according to an exampleembodiment.

DETAILED DESCRIPTION

FIG. 1 is a diagram showing two nodes 102, 104 in wireless (or unguided)communication according to an example embodiment. The nodes 102, 104 mayinclude, for example, IEEE 802.11 wireless local area network (WLAN)nodes (such as a station 102 and an access point 104), IEEE 802.16Worldwide inter-Operability for Microwave Access (WiMAX) nodes, IEEE802.15 Bluetooth nodes, or cellular telephones/smartphones and basestations, according to various example embodiments. While theterminology of IEEE 802.11 is used herein, the techniques and methodsdescribed herein are applicable to a wide range of wireless (orunguided) communication technologies.

Station 102 may include a station or apparatus in wireless communicationwith an access point 104. The station 102 may disconnected from anyexternal power source and rely on battery power. The station 102 mayhave limited battery power, and it may be desirable to reduce the use ofthe battery power. At times, it may desirable for the station 102 toperform techniques to reduce the use of battery power.

The nodes 102, 104 may be capable of communication using both multipleinput, multiple output (MIMO) techniques, in which the transmitting node102, 104 has two or more transmitters, and sends two or more unique datastreams or signals in the same frequency, and the receiving nodecombines the multiple streams or signals to recover the originaltransmitted streams, as well as single input, single output (SISO)techniques, in which only a single data stream or signal is transmitted.MIMO may be advantageous by sending or transmitting multiple outputs,creating spatial multiplexing to allow for transmission and reception ofa better signal. Similarly, MIMO may receive at multiple inputs orantennas, maximizing the possibility of receiving a strong signal.However, MIMO may consume more power than SISO at both the transmittingnode by transmitting two or more streams or signals, and at thereceiving node by processing the two or more streams or signals; attimes, it may be helpful to transition to SISO to conserve power.

The access point 102 may transition from MIMO to SISO to save powerunder various conditions. For example, the station 102 may transition toan IEEE 802.11 power save mode, and transition from MIMO to SISOconcurrently with transitioning to the power save mode. The station 102may also transition from MIMO to SISO when entering a power save modeusing unscheduled automatic power save delivery (U-APSD). The station102 may also selectively use MIMO for certain types of traffic, such asvoice and video traffic, while using SISO for other types of traffic,such as best effort and background traffic. The station 102 may alsotransition from MIMO to SISO based on remaining battery power, and enterthe MIMO communication when battery power is low, or has reached orpassed a predetermined threshold. The station 102 may also communicatein MIMO or SISO based on a transmission queue depth; when thetransmission queue depth is high, indicating that there are many packetsthat need to be sent out or transmitted, the station 102 may communicatein MIMO to ensure a high effective data rate, whereas when thetransmission depth is low, the station 102 may transition to, orcommunicate in, SISO, to reduce power consumption.

FIG. 2 is a vertical time sequence diagram showing communication betweenthe nodes 102, 104 according to an example embodiment. The diagram showscommunication between the station 102 and the access point 104.

The station 102 and the access point 104 may engage in associationprocedures. The station 102 and access point 104 may have engaged inprobe request and probe response communications to negotiate securityparameters, as well as authentication request and authenticationresponse communications to negotiate authentication parameters and/orauthenticate the station 102. The station 102 may send an associationrequest 202 to the access point 104. The association request 202 mayinclude a management frame such as the management frame 300 shown inFIG. 3. The association request 202 and/or management frame 300 mayinclude, for example, a medium access control (MAC) header 302, a framebody 304, and a frame check sequence (FCS) 306. The MAC header 302 mayinclude a frame control field 308, a duration field 310, a destinationaddress (DA) field 312, a source address (SA) field 314, a basic serviceset identification (BSSID) field 316, a sequence control field 318, anda high throughput (HT) control field 320.

The frame body 304 of the association request 202 may include, forexample, a capability subfield, a listen interval subfield, a serviceset identifier (SSID) subfield, a supported rates subfield, an extendedsupported rates subfield, a power capability subfield, a supportedchannels subfield, a robust security network (RSN) subfield, a qualityof service (QoS) capability subfield, an HT capabilities subfield, a20/40 basic service set (BSS) subfield, an extended capabilitiessubfield, and any vendor-specific information elements. In an exampleembodiment in which the station 102 uses MIMO only for certain types oftraffic, such as voice and video traffic (discussed below), the framebody 304 of the association request 202 may also include a subfieldand/or element ID indicating which types of traffic will be sent usingMIMO and/or which types will be sent using SISO. The subfield and/orelement ID indicating which types of traffic will be sent using MIMO mayidentify only the traffic types which will be sent using MIMO, leavingthe SISO traffic types to be inferred by their lack of identification,may identify only the traffic types which will be sent using SISO,leaving the MIMO traffic types to be inferred by their lack ofidentification, may identify a priority level above or below whichtraffic will be sent using either MIMO or SISO, or may specificallyidentify which traffic types will be sent using each of MIMO and SISO,according to various example embodiments.

The association request 202 may indicate a request by the station 102 toassociate with a wireless network served by the access point 104. Theassociation request 202 may also indicate the station 102's MIMO and/orSISO communication capabilities (which may, for example, be included inthe HT capabilities subfield of the frame body 304).

The access point 104 may respond to the association request 202 bysending an association response 204. The association response 204 mayalso include a management frame such as the management frame 300 shownin FIG. 3. The association response 204 and/or management frame 300 mayinclude, for example, the medium access control (MAC) header 302, theframe body 304, and the frame check sequence (FCS) 306. The MAC header302 may include the frame control field 308, the duration field 310, thedestination address (DA) field 312, the source address (SA) field 314,the basic service set identification (BSSID) field 316, the sequencecontrol field 318, and the high throughput (HT) control field 320.

The frame body 304 of the association response 204 may include, forexample, a capability subfield, a status code subfield, an associationidentifier (AID) subfield, a supported rates subfield, an extendedsupported rates subfield, an enhanced distributed channel access (EDCA)parameter set subfield, an HT capabilities subfield, an HT operationsubfield, a 20/40 BSS coexistence subfield, an overlapping BSS scanparameters, subfield, an extended capabilities subfield, and anyvendor-specific information elements or subfields.

The association response 204 may grant the request by the station 102 toassociate with and/or enter the wireless network served by the accesspoint 104. The association response 204 may also indicate that theaccess point 104 is capable of communicating in both MIMO and SISO modes(which may, for example, be included in the HT capabilities subfield ofthe frame body 304). The access point 104 may also advertise or indicatewhether it is capable of MIMO communication in beacon frames and/or theprobe response frame(s).

After the association has been completed by the exchange of theassociation request 202 and the association response 204, the station102 and the access point 104 may engage in MIMO communication 206. Thestation 102 and access point 104 may engage in MIMO communication 206 bysending or transmitting signals, which may include data and/or controlinformation, via multiple outputs or antennas, and/or by receivingsignals via multiple inputs or antennas. During the MIMO communication,the access point 104 may indicate its capability of supporting a lowpower mode and/or unscheduled automatic power save delivery (U-APSD).These capabilities may be indicated, for example, in periodic beaconframes sent or transmitted by the access point 104.

While this MIMO communication is ongoing, the station 102 may experiencea transition trigger 208. The transition trigger 208 may include anytrigger or determination to enter the SISO mode. The transition trigger208 may include, for example, a determination to enter a power savemode, a determination that the battery power of the battery in thestation 102 is low, or a determination that a transmission queue depthof the station 102 is sufficiently low to enter SISO communication.

Upon the transition trigger, the station 102 may send a transitionmessage 210 to the access point 104. The transition message 210 mayindicate that the station 102 will transition from the MIMOcommunication to the SISO communication. In an example embodiment, theindication of the transition may be included in an action frame whichmay also indicate that the station 102 is entering a low-power state orU-APSD. The transition message 210 may include an action frame. Thetransition message 210 may include a NULL or QNULL frame, such as a dataframe with a subtype set to Null (no data) or QoS Null (no data).

FIG. 4 is a diagram showing a data frame 400 according to an exampleembodiment. The transition message 210 sent by the station 102 to theaccess point 104 to indicate the transition from MIMO communication toSISO communication may include the fields shown in the data frame 400 ofFIG. 4. The data frame 400 and/or transition message 210 may include aMAC header 402 and a frame check sequence 404. The MAC header 402 mayinclude a frame control field 406, a duration field 408, an address 1field 410, an address 2 field 412, an address 3 field 414, a sequencecontrol field 416, an address 4 field 418, and a QoS control field 420.The address 1 field 410 may include the address of the intendedrecipient(s) of the data frame 400 or transition message 210, such asthe access point 204, and the address 2 field 412 may include theaddress of the station 102 that is transmitting the data frame 400 oftransition message 210. The QoS control field 420 may indicate that thedata frame 400 and/or transition message 210 is a transition message andthat the access point 102 is transitioning from MIMO to SISO, such as byincluding a subtype value corresponding to Null (no data) or QoS Null(no data), according to example embodiments.

The access point 104 may receive the transition message 210 and send anacknowledgement message, such as a transition acknowledgement 212 to thestation 102. The transition acknowledgement 212 may have a similarformat to the transition message 210, such as by including the fields ofthe data frame 400. The QoS control field 420 of the transitionacknowledgment 212 may indicate that the data frame 400 and/ortransition acknowledgment 412 is a transition acknowledgment, such as byincluding a subtype value corresponding to CF-Ack (no data),CF-Ack+CF-Poll (no data), QoS CF-Poll (no data), or QoS CF-Ack+CF-Poll(no data), according to example embodiments.

The transition acknowledgment 212 and/or data frame 400 sent by theaccess point 104 to the station 102 may indicate that the access point104 has received and accurately processed the transition message 210,and is prepared for the station 102 to transition into SISO and commencecommunication in SISO. Upon receipt of the transition acknowledgement212 from the access point 104, the station 102 may engage in SISOcommunication 214 with the access point 104. In SISO communication 214,the station 102, and/or the access point 104, may communicate by sendingdata using only a single output or antenna to send messages, and alsousing only a single input or antenna to receive messages. The station102 and the access point 104 may engage in SISO communication 214 untilthe station 102 determines to return to MIMO communication 216. Thestation 102 may determine to return to MIMO communication 216 based onevents which mirror the events which trigger the transition into SISO,such as battery power being high enough or transition queue depth beinghigh enough.

In the example of transitioning to SISO communication 214 based onentering power save mode, the station 102 may engage in SISOcommunication while in the power save mode. In the power save mode, thestation 102 may sleep during most of the time that the access point 104is communicating with other nodes, but may wake up, such as by poweringon the receiver, during expected reception times (which may be indicatedby a beacon transmitted by the access point 104), to determine whetherdata addressed for the station 102 is scheduled to be sent by the accesspoint 104 to the station 102. The access point 104 may buffer packetsdestined for the station 102 during the station's 102 sleep mode, andmay send the buffered packets to the station 102 when the station 102periodically wakes. If the beacon frame does indicate that data isscheduled to be sent from the access point 104 to the station 102, thestation 102 may stay awake and wait for the data or frame, or may wakeup at a time indicated by the beacon to receive and process the data orframe. If the beacon does not indicate that the access point 104 will besending data to the station 102, the station 102 may remain asleep untilthe next beacon frame or scheduled reception time.

In the SISO communication 214 during U-APSD, the station 102 may spendtime in a dozing state which consumes less power. The station 102 maydoze until specific times when the access point 104 is scheduled to sendframes or packets to the station 102. The station 102 may also requestthe access point 104 to send buffered frames by sending a trigger frameindicating the request to send the buffered frames; the trigger framemay be included in an action frame, according to an example embodiment.During the times when the access point 104 is scheduled to send framesor packets to the station 102, the station 102 may awake to receive theframes or packets. If the station 102 is entering the SISO communicationor transitioning from MIMO communication to SISO communication based onremaining battery power, the station 102 may continuously orperiodically monitor the battery power. The station 102 may compare themeasured battery power to a threshold; when the battery power is at orbelow the threshold, the station 102 may determine to transition fromMIMO communication to SISO communication. Upon making the determinationbased on the comparison of the measured battery power to the thresholdlevel, the station 102 may send the transition message 210 to the accesspoint 104, and upon receipt of the transition acknowledgement 212transition from the access point 104, cease or transition from MIMOcommunication and commence or transition to the SISO communication.

In the example of transitioning based on the transmission queue depth,the station 102 may monitor and/or compare a transmission queue depth toa threshold. The transmission queue depth may be based on a number ofpackets or frames ready to be sent by the station 102 to the accesspoint 104. The station 102 may buffer frames or packets in a memory, andbe ready to send the packets or frames to the access point 104 duringtimes that the access point 104 schedules for the station 102 to senddata to the access point 104. When the transmission queue depth has metor gone below the transmission queue depth threshold, the station 102may determine to transition from MIMO communication to SISOcommunication. Upon making the determination to transition from MIMOcommunication to SISO communication, the station 102 may send thetransition message 210 to the access point 104. Upon receiving thetransition acknowledgement 212 from the access point 104, the station102 may transition from MIMO communication to SISO communication andcommence SISO communication 214 with the access point 104.

In the example in which MIMO mode is used for only certain types oftraffic, the station 102 may not need to send the transition message 210or receive to the access point 104 or receive the transitionacknowledgement 212 from the access point 104. In this example, thestation 102 and access point 104 may have negotiated the parameters forMIMO and SISO communication during the association. For example, theassociation request message 202 may have previously indicated for whichtypes of traffic the station 102 will communicate using MIMO and forwhich the station 102 will communicate using SISO. For example, theassociation request 202 (which may have the format of the managementframe 300) may indicate for which traffic types the station 102 will useMIMO for which traffic types the station 102 will use SISO. Theindication of which traffic types will use MIMO and which traffic typeswill use SISO may be included in a subfield and/or element ID of theframe body 304 of the association request 202. For example, the subfieldand/or element ID of the frame body 304 may indicate that the station102 may communicate with the access point 104 using MIMO for voicetraffic and video traffic but will use SISO for best effort traffic andbackground traffic. Thus, the station 102 and access point 104 mayalready understand during the MIMO communication and/or SISOcommunication that the station 102 will be communicating in theindicated type of communication protocol for the indicated type oftraffic. The station 102 and access point 104 may not need to engageexclusively in MIMO communication 206 or SISO communication 214, but mayengage in blended communication techniques with MIMO communication beingused for higher priority traffic types such as voice and video traffic,and SISO communication for lower priority traffic such as best effortand background traffic. In an example embodiment, the station 102 maydynamically change which traffic types use MIMO communication and whichtraffic types use SISO communication; the station 102 may, for example,send an action frame or management frame to the access point 104indicating which types of traffic will use MIMO and/or which types oftraffic will use SISO.

FIG. 5 is a block diagram of an apparatus 500 according to an exampleembodiment. The apparatus 500 may include a wireless node such as thestation 102, and may include an IEEE 802.11 node, IEEE 802.16 nodes,IEEE 802.15 node, or cellular telephone/smartphone, netbook, tablet PC,iPad, or laptop computer, as non-limiting examples. The apparatus 500may include a controller 502 and memory 504. The memory 504 may storedata and instructions. The controller 502 may execute the instructionsstored in the memory 504 to perform any of the tasks, methods, orfunctions described herein. The apparatus 500 may also include arechargeable or non-rechargeable battery 506. The controller 502 maymonitor the power level of the battery 506 to determine whether totransition to from the MIMO communication to the SISO communication, asdescribed above.

The apparatus 500 may also include a baseband processor 508. Thebaseband processor may convert between data generated or processed bythe controller 502 and baseband signals received or transmitted by atransceiver 510 according to a communication standard, such as IEEE802.11, IEEE 802.16, IEEE 802.15, or any cellular communicationtechnology. The apparatus 500 may include the transceiver 500, which mayconvert between the baseband signals and radio frequency (RF) signals,and serve as the physical interface for communicating with otherwireless devices, such as the access point 104.

Implementations of the various techniques described herein may beimplemented in digital electronic circuitry, or in computer hardware,firmware, software, or in combinations of them. Implementations mayimplemented as a computer program product, i.e., a computer programtangibly embodied in an information carrier, e.g., in a machine-readablestorage device, for execution by, or to control the operation of, dataprocessing apparatus, e.g., a programmable processor, a computer, ormultiple computers. A computer program to execute the tasks, methods, orfunctions described above, can be written in any form of programminglanguage, including compiled or interpreted languages, and can bedeployed in any form, including as a stand-alone program or as a module,component, subroutine, or other unit suitable for use in a computingenvironment. A computer program can be deployed to be executed on onecomputer or on multiple computers at one site or distributed acrossmultiple sites and interconnected by a communication network.

Method steps may be performed by one or more programmable processorsexecuting a computer program to perform functions by operating on inputdata and generating output. Method steps also may be performed by, andan apparatus may be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors (or controllers) suitable for the execution of a computerprogram include, by way of example, both general and special purposemicroprocessors, and any one or more processors of any kind of digitalcomputer. Generally, a processor will receive instructions and data froma non-transitory, computer-readable read-only memory or anon-transitory, computer-readable random access memory, or both.Elements of a computer may include at least one processor for executinginstructions and one or more memory devices for storing instructions anddata. Generally, a computer also may include, or be operatively coupledto receive data from or transfer data to, or both, one or more massstorage devices for storing data, e.g., magnetic, magneto-optical disks,or optical disks. Information carriers suitable for embodying computerprogram instructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, e.g., EPROM,EEPROM, and flash memory devices; magnetic disks, e.g., internal harddisks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The processor and the memory may be supplemented by, orincorporated in special purpose logic circuitry.

To provide for interaction with a user, implementations may beimplemented on a computer having a display device, e.g., a cathode raytube (CRT) or liquid crystal display (LCD) monitor, for displayinginformation to the user and a keyboard and a pointing device, e.g., amouse or a trackball, by which the user can provide input to thecomputer. Other kinds of devices can be used to provide for interactionwith a user as well; for example, feedback provided to the user can beany form of sensory feedback, e.g., visual feedback, auditory feedback,or tactile feedback; and input from the user can be received in anyform, including acoustic, speech, or tactile input.

Implementations may be implemented in a computing system that includes aback-end component, e.g., as a data server, or that includes amiddleware component, e.g., an application server, or that includes afront-end component, e.g., a client computer having a graphical userinterface or a Web browser through which a user can interact with animplementation, or any combination of such back-end, middleware, orfront-end components. Components may be interconnected by any form ormedium of digital data communication, e.g., a communication network.Examples of communication networks include a local area network (LAN)and a wide area network (WAN), e.g., the Internet.

While certain features of the described implementations have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the embodiments of the invention.

1. An apparatus comprising: at least one processor; and at least onememory comprising computer-executable code that, when executed by theprocessor, is configured to cause the apparatus to: send a message to anode in wireless communication with the apparatus, the messageindicating a transition by the apparatus from multiple-inputmultiple-output (MIMO) to single-input single-output (SISO); andtransition from wireless MIMO communication with the node to wirelessSISO communication with the node after sending the message to the node.2. The apparatus of claim 1, wherein the computer-executable code isconfigured to cause the apparatus to transition from the wireless MIMOcommunication with the node to the wireless SISO communication with thenode after receiving an acknowledgment from the node acknowledging themessage indicating the transition.
 3. The apparatus of claim 1, whereinthe computer-executable code is further configured to cause theapparatus to: determine to enter a power save mode; determine totransition from the MIMO to the SISO based on determining to enter thepower save mode, wherein the apparatus is configured to send the messageand transition from the MIMO communication to the SISO communicationbased on the determining to transition from the MIMO to the SISO.
 4. Theapparatus of claim 1, wherein the computer-executable code is furtherconfigured to cause the apparatus to: determine to transition from theMIMO to the SISO based on a measured level of battery power in theapparatus, wherein the apparatus is configured to send the message andtransition from the MIMO communication to the SISO communication basedon the determining.
 5. The apparatus of claim 1, wherein thecomputer-executable code is further configured to cause the apparatusto: determine to transition from the MIMO to the SISO based on a depthof a transmission queue, the transmission queue storing data to be sentfrom the apparatus to the node, wherein the apparatus is configured tosend the message and transition from the MIMO communication to the SISOcommunication based on the determining.
 6. The apparatus of claim 1,wherein the message comprises a frame indicating that the apparatus isentering a power save mode and the transition by the apparatus frommultiple-input multiple-output (MIMO) to single-input single-output(SISO).
 7. The apparatus of claim 1, wherein the computer-executablecode is further configured to cause the apparatus to associate with theaccess point, the associating including receiving a message from theaccess point indicating that the access point supports MIMOcommunication.
 8. The apparatus of claim 1, wherein thecomputer-executable code is further configured to cause the apparatusto: send a message to the node indicating a transition by the apparatusback from SISO to MIMO; and transition back from wireless SISOcommunication to wireless MIMO communication with the node after sendingthe message indicating the transition back from SISO to MIMO.
 9. Anapparatus comprising: at least one processor; and at least one memorycomprising computer-executable code that, when executed by theprocessor, is configured to cause the apparatus to: wirelesslycommunicate with a node according to a multiple-input multiple-output(MIMO) communication protocol for at least a first traffic type; andwirelessly communicate with the node according to a single-inputsingle-output (SISO) communication protocol for at least a secondtraffic type.
 10. The apparatus of claim 9, wherein thecomputer-executable code is further configured to cause the apparatusto: determine to transition from the MIMO to the SISO based on achanging priority level of traffic sent between the apparatus and thenode, wherein the apparatus is configured to transition from the MIMOcommunication to the SISO communication based on the determining. 11.The apparatus of claim 9 wherein the computer-executable code isconfigured to cause the apparatus to: communicate with a wireless nodeaccording to the MIMO communication protocol for voice and videotraffic; and communicate with the wireless node according to the SISOcommunication protocol for best effort and background traffic.
 12. Theapparatus of claim 9, wherein the computer-executable code is furtherconfigured to cause the apparatus to send an association request frameto the node, the association request frame indicating the first traffictype for which the apparatus will communicate according to the MIMOprotocol and the second traffic type for which the apparatus willcommunicate according to the SISO protocol.
 13. The apparatus of claim9, wherein the computer-executable code is further configured to causethe apparatus to send an updated MIMO frame to the node, the updatedMIMO frame indicating which traffic types the apparatus will communicatein using MIMO.
 14. A non-transitory, computer-readable medium comprisingcomputer-executable code stored thereon that, when executed by a dataprocessing apparatus, is configured to cause the data processingapparatus to: send a message to a node in wireless communication withthe data processing apparatus, the message indicating a transition bythe apparatus from multiple-input multiple-output (MIMO) to single-inputsingle-output (SISO); and transition from wireless MIMO communicationwith the node to wireless SISO communication with the node after sendingthe message to the node.
 15. The computer-readable medium of claim 14,wherein the computer-executable code is configured to cause theapparatus to transition from the wireless MIMO communication with thenode to the wireless SISO communication with the node after receiving anacknowledgment from the node acknowledging the message indicating thetransition.
 16. The computer-readable medium of claim 14, wherein thecomputer-executable code is configured to cause the data processingapparatus to: determine to enter a power save mode; determine totransition from the MIMO to the SISO based on determining to enter thepower save mode, and send the message and transition from the MIMOcommunication to the SISO communication based on the determining totransition from the MIMO to the SISO.
 17. The computer-readable mediumof claim 14, wherein the computer-executable code is further configuredto cause the data processing apparatus to: determine to transition fromthe MIMO to the SISO based on a measured level of battery power in theapparatus, wherein the sending the message and transitioning from theMIMO communication to the SISO communication is based on thedetermining.
 18. The computer-readable medium of claim 14, wherein thecomputer-executable code is further configured to cause the dataprocessing apparatus to: determine to transition from the MIMO to theSISO based on a depth of a transmission queue, the transmission queuestoring data to be sent from the apparatus to the node, wherein sendingthe message and transitioning from the MIMO communication to the SISOcommunication is based on the determining.
 19. The computer-readablemedium of claim 14, wherein the message comprises a null frameindicating that the apparatus is entering a power save mode and thetransition by the data processing apparatus from multiple-inputmultiple-output (MIMO) to single-input single-output (SISO).
 20. Thecomputer-readable medium of claim 14, wherein the computer-executablecode is further configured to cause the data processing apparatus toassociate with the access point, the associating including receiving amessage from the access point indicating that the access point supportsMIMO communication.